89 audi 100, fan problems

Ok, My 89 audi is having some probelms. I think it was yesterday, i
pulled into my driveway after work and noticed the fan, the one right
behind the radiator, wasn't stopping. I figured that it would stop
within 5-10 minutes. I came back out 15 minutes later and the fan was
still running. I started my vehicle to make sure the battery wouldn't
die, and then turned off my car again. Once again i waited for another
15 minutes, with the car off, but the fan kept on runnning. So now
whenever i want to drive my car i have to pull the battery so the fan
will stop. Please any ideas will help.

Thank you,
Jimmie